GTE Omni Si Database Technical Practices Issue 1 Manual
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TL-130500-1001 THIS PAGE IS INTENTIONALLY LEFT BLANK. S-2748187SVR 5210
SVR 5210TL-130500-1001 RELEASE28.0 RLTs (Release Link Trunks) are used to minimize the LINK TRUNKS number of interconnecting trunks required to connect a main system with branch systems for CAS operation and to provide the control and features required by this integral configuration. Both the CAS main and the branch must have the special capability of using RLTs. Additional hardware and revised data base distribution are required to incorporate RLTs into the system. However, RLTs are not tied up for the duration of the CAS call but are available when needed. They allow the interchange of control functions between two systems without the need for any additional interconnections and appear transparent to the users. Incoming calls to the branch PABX are identified by differential audible tones heard by both end users and through seizure of the RLT associated with the main system. An audible ring is returned from the PABX station to the telephone instrument. The CO trunk-to-station connection at the branch is still set up and ringing continues at the station.The attendant “holds” the caller at the branch, and connects the call. The RLT releases to idle condition for RLT-2WGS (Wire Ground Start). (The branch end RLT-2WGS should provide open tip and ring leads to the main PABX end during the idle state). When the call is answered, the branch end RLT-2WGS stops ringing within 100 msec. of receiving the answer signal. Ringing is tripped during both the silent and ringing intervals. The branch end PABX detects the answer signal from the RLT-2WGS and passes it to the connecting circuit (i.e., PABX-CO trunk) to cause CO ringing to trip and cut through the transmission path for talking. When an answer is detected, the branch PABX times for 300 msec. and then transmits, via the RLT-2WGS, through the appropriate call information tone to the CAS attendant, followed by cut-through of the transmission path between the calling party and the RLT-2WGS. After answer and until disconnect, the branch end RLT-2WGS provide up to 425 ohms resistance to ground on the tip lead, and -48 VDC loop battery through up to 425 ohms resistance on the ring lead. 8187S-275
TL-130500-1001 S-276n n ni OMNI PBAX (MAIN) 1BRANCHES CENTRAL OFFICE TRUNKS Figure 28.1Release Link TrunksIf a call is directed to an idle station but the station is not answered within the selected time-out interval, the system recalls the attendant by means of a preselected idle RLT. On recalls, the appropriate audible signals are extended to the attendant to identify the type of call. The tone is heard only by the attendant because the system delays cut-through long enough to permit any required audible signal to be sent to the main location before the calling party is connected. If the station is not answered before the attendant answers, the seized PRLT signals the attendant with the appropriate audible tone. The call is then reconfigured to a three-way mode in which the local station continues to ring while the attendant and the trunk party converse over ringback tone. If the trunk party does not wish to wait for the selected line to answer, the attendant flashes off the original called number. The attendant then redirects the call by a second flash and redialing. Alternatively, the station can answer after the attendant has been recalled; the attendant then releases the PRLT and causes the trunk and line to remain connected while the PRLT is made available for reuse. The same procedure applies when the line rings for an additional recall period. 8187SW 5210
TL-130500-1001 The functions of the PRLTs can be summarized as follows: The branch system uses the PRLT to send supervisory and information signals to the CAS Main, and receives supervisory and address signals from the CAS equipment to direct call switching at the branch location. Only the branch can seize the PRLT to initiate the sequence. The system can extend stations or tie trunks to outgoing trunks via the PRLT if this feature is required. The system supports a maximum of 16 PRLTs. Refer to the system functional block diagram found in TL-130300-1001. The PRLT trunks are connected into the system via an FB-17251 -A PRLT card. Each card can support four PRLTs.Each PRLT can be dialed up for testing. The CAS branch system provides the cross-connecting arrangements so that telephones can be used for terminating the PRLTs at the branch location. This arrangement permits calls to be answered locally when the equipment at the main location fails, or the trunk facilities fail and no local console has been provided. SVR 5210Each PRLT in the system has an assigned access number permitting the main location to make loop-around test calls to verify performance of both PRLT and main locations are being properly done. The main location accesses the branch system via a designated Tie trunk. The branch system is directed by dialing the PRLT access number to connect the Tie trunk to the selected PRLT for extension back to the main location. Two lOO-msec bursts of tones signal the CAS attendant of a test call. Test calls can also be originated from the branch location by special stations class-marked in the data base as maintenance lines. During the talking state, the RLT-2WGS circuit interprets a substained increase in the external DC resistance across the T and R leads from less than 1,300 ohms to greater than 20 kilohms for greater than 1 second as a disconnect indication. If the calling party abandons the call before answer supervision is received from the CAS Main location, the RLT-2WGS send a disconnect signal to the call distributor by opening the T and Rleads. 8187S-277
TL-130500-1001 The manner in which the call is completed varies according to the status of the local line selected. If the call is successfully terminated, immediate ringback tone is transmitted to the CAS Main and the CAS attendant operates the RELEASE pushbutton. The RLT interprets this as an on-hook condition, the system then reconfigures the call and connects the incoming trunk to the destination station. The four-wire E&M RLT provides audio frequency transmission via the T, R and Tl, Rl leads, while supervisory signals are transmitted over the M lead (outgoing) and the E lead (incoming). The T, R and Tl, Rl leads do not carry DC signals. The CAS Branch PABX trunk circuit sends a seizure by replacing the ground potential on the M lead by -48 VDC battery potential. The seizure is received at the CAS Main location as a change of state on the E lead from open to ground. The E lead at one end of the interconnecting facility always indicates the state of the M lead at the other end of the facility. Disconnect at either end of the facility is signaled by connecting ground to the M lead at the disconnecting end. The other end of the facility receives the disconnect as a change of state on the E lead from ground to open. The four-wire E&M RLT reflects an idle state at the branch PABX as a ground on the M lead, causing the CAS Main to receive an open on the E lead. The CAS Branch PABX reflects an outgoing seizure condition by applying -48 VDC battery to the M lead (removing ground). After sending a seizure, the branch PABX should interpret the appearance of ground on the E lead as answer supervision indication from the main location. Upon receipt of answer supervision, the branch PABX performs the following functions: l Return answer supervision (trips ringing) to the CO trunk (if involved). 0 Time for 300 msec, followed by transmittal of the appropriate call information tone to the centralized attendant, followed by cut-through of the voice transmission path between the calling party (i.e., CO trunk) and the attendant. During the talking state, the branch PABX should maintain -48 VDC battery on the M lead and continue to monitor ground on the E lead. During the talking state, the branch PABX interprets a momentary open of the E lead (i.e., 300 to 1,000 msec) as a flash. During the talking state, the branch PABX interprets an E lead open of greater than 1 second as a disconnect signal. If the calling party abandons the call before the attendant answers the call, the branch PABX replaces the -48 VDC battery on the M lead with ground, thereby transmitting a disconnect indication to the main location. S-2788187SVR 5210
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TL-130500-1001 29.0 The Tl digital trunk link allows the system to receive and transmit time-division-multiplexed Tl carrier data to and from a channel bank at the far end. A Tl digital data link can support 24 channels of multiplexed Tl-type data. The two-line (transmit and receive) Tl trunk link provides the same traffic capabilities as 24 individual analog trunk lines. The Tl digital trunk link (Figure 29.1) consists of the Tl interface cards at the system end, a channel bank at the far end, and a Tl span in between. I .TRANSMISSIONFACILITY SPANLINEISVR 5210 Figure 29.1Tl-Type Digital Trunk Link 8187S-281
TL-130500-1001 The Tl interface is compatible with WECO D2 and D3 signaling format channel banks or Siemens Transmissions Systems 9002A (24) or 9002B (48) channel banks at the far end. The far-end channel bank interfaces with loop-start, ground-start, or E&Mtrunks that can be connected to any standard telephone and most data terminals, to a system, or to a CO that supports Tl-type communications. Two systems can be connected via a Tllink without the use of a channel bank at either end. The Tlinterface is joined directly to the local terminating shelf repeater and does not require a channel bank or A/D to D/A converters in the system end (Figure 29.1). Supervisory signaling information is transmitted every sixth frame. During the signaling frame, the least-significant digit is borrowed from the voice information coding and used to indicate the signaling condition of each channel. Alternate signaling frames are designated as A and B, respectively, called A and B signaling. When a customer-related interface is used, such as a FX ground start or FX loop start, the A signaling frame provides on-hook/off-hook information. The B signaling frame provides ringing information and special conditions. S-282CAUTION Because the removal of a loop-start channel at the CO is not detected by the Tl-type interface it is recommended that the use of loop-stsrt channels for Tl interface be avoided. The removal of a loop-start channel unit at the CO is not detected by the Tl-type interface cards. Therefore, it is recommended that use of the loop-start channel interface be avoided for Tl applications. Removal of a ground-start channel unit at the CO causes the GD (Ground-Detected) sense point, bit 7, in the FX trunk sense word to become true, making the associated trunk busy to the system. When this occurs, the associated trunk-busy lamp on the Attendant Console lights. 8187SVR 5210